Glass fibers have long been noted for their insulating value. However, depending upon the end use of the insulation there are disadvantages to be found in glass fiber insulation now in general use.
It is characterisitc of fibrous insulation that the respective fibers are bonded to one another by a suitable binder system which normally consists of a phenolic liquid resole resin or a conventional phenolic-formaldehyde resin in combination with various additives. These additives are used to improve either the process characteristics of the binder system or to improve the finished fiber glass product characteristics. The resole resins may be made by partial condensation of a phenol with a molar excess of an aldehyde in alkaline solution. In most cases the type of resole used in one prepared by condensing about one mole of phenol with about 2.0 to 3.0 moles of formaldehyde. An alkaline catalyst may be used and may comprise any water soluble alkali metal hydroxide or alkali earth compound. Catalysts such as sodium hydroxide, sodium carbonate, calcium hydroxide and barium hydroxide have been successfully employed.
This type of organic liquid resole resin when applied to a fiber glass mass or an insulation in concentrations of 1 to 20% of the total mass, is readily susceptible to flameless combustion or "punking" when exposed to temperatures in excess of 425.degree. F. (209.5.degree. C.). Punking, of course, is a term of art used to denote the comparatively rapid flameless oxidation of the binder with a concomittant generation of heat. Odors and fumes given off by such thermal decomposition are offensive, potentially hazardous and are capable of discoloring and staining adjacent materials. Furthermore, punking may be associated with exothermic reactions which increase temperatures through the thickness of the insulation causing a fusing or devitrification of the glass fibers and possibly creating a fire hazard. Once devitrification has occurred the insulation is usually incapable of thermally insulating an associated object and may warp and pull away from the very object it was intended to insulate. Furthermore, devitrification of the glass fibers causes the fiber glass product to lose its structural integrity to the extent that the vibrations and impacts occurring during normal usage may cause dusting problems. In an extreme case the normal vibrations and impacts may dislodge the insulation causing it to become a personal safety hazard in the working environment.
In an effort to reduce punking the art has attempted to increase the punk resistance of the binder systems used and to more nearly align the properties of the binder system with the properties of the glass fiber by reacting nitrogenous substances such as melamine, dicyandiamide, urea, thiourea, biurea, guanidine and similar compounds with phenol-aldehyde partial condensation products of the resole type. Although the incorporation of such nitrogenous compounds improves the punk resistance and overall thermal stability of the binder system, products composed of glass fibers in association with such binder systems are still not suitable for use in environments approaching the limits of the heat stability of the glass fiber itself.
Commercially available "anti-punk" phenolic-formaldehyde resins containing additives such as dicyandiamide, melamine, urea or combinations thereof, which are co-reacted at the time of resin manufacture, possess satisfactory "anti-punk" properties but generally lack stability during storage in comparison to a conventional phenolicformaldehyde resin, e.g., certain components precipitate out of the resin solution or water dilutability is lost during storage. Both these reductions in stability increase production difficulties. Also, it is inconvenient to store anti-punk resins for fibrous products requiring same and to separately store conventional phenolicformaldehyde resins for products not requiring anti-punk characteristics. Finally, the cost of commercially available anti-punk phenolic-formaldehyde resins has increased dramatically in recent years thereby reducing its attractiveness.
The addition of anti-punk ingredients to a conventional phenolic-formaldehyde resin by a fiber glass manufacturer just prior to production use would make the anti-punk binder more flexible in processing and more economical. The manufacturer would be able to add the optimal amount of anti-punk ingredient that would satisfy the needs of a specific product; the need depending on the use of the finished product. Also by adding the anti-punk ingredient to a conventional phenolic-formaldehyde resin the fiber glass manufacturer has more choices in what resin to purchase as there are many more conventional resins commercially available than anti-punk resins. This broader purchasing range gives the manufacturer an economic advantage. Conventional phenolic-formaldehyde resins, for example, are traditionally lower cost than anti-punk phenolic-formaldehyde resin. Therefore if a low cost anti-punk ingredient is used in the binder system, the anti-punk binder system would be lower in cost overall.
The addition of the nitrogen containing compounds after the resin manufacture is often hampered by the handling characteristics of the nitrogen containing compounds. Urea, although readily water soluble and economical, when added to a binder system containing a standard commercially available liquid resole thermal insulation resin, presents a potential emission problem due to the high volatility of urea. Melamine and/or dicyandiamide combinations are expensive to purchase and pose post-resin manufacture addition problems such as stability.
It is imperative that any binder system satisfy not only the anti-punking requirement but also satisfy the other product requirements, for example, many products must possess moisture resistance and compressive strength.
There thus exists a need for an economical and relatively simple way to impart "anti-punk" properties to a conventional phenolic resole resin thereby avoiding the impediments cited above.